1. Field of the Invention
The invention relates to methodologies to analyze breast density based on magnetic resonance imaging (MRI).
2. Description of the Prior Art
Mammary gland architecture may play an important role in determining the susceptibility of developing breast cancer. The most well-studied parameter is mammographic density, evaluated as the percentage of dense tissue area over the total breast area on mammograms. There are numerous studies reporting mammographic density as a strong risk factor; the higher the percentage, the higher the breast cancer risk. Increased density over time has also been shown to be associated with higher cancer incidence. There is also evidence suggesting that the relative distribution of adipose and fibroglandular tissue (referred as the breast parenchymal pattern in this specification) is involved in cancer development. The adipose tissue that is abundantly present around the ductal epithelium of the mammary gland may function as a slow release depot for lipid-soluble carcinogenic agents, and thus may affect cancer risk. However, the relationship between parenchymal pattern and cancer risk has never been reported, possibly due to the lack of both the imaging modality necessary to reveal the distribution pattern and the appropriate analysis methods.
Several studies have applied texture analysis to analyze the distribution pattern of the projected dense tissue on mammograms, and shown differences between women with invasive cancer and women without cancer. There are also differences between high-risk women carrying the BRCA1 and BRCA2 gene and low-risk women, which is possibly due to lobular branching promoted by these genes. Since the mammogram is a two-dimensional (two dimensional) projection image, texture analysis can be used to characterize the amount and/or the heterogeneity/homogeneity of dense tissue. However, as these features arise in part from the way that tissues overlap on the projected image, the analyzed parameters may be affected by different positioning of the breast and the degrees of compression.
What is needed is a three-dimensional imaging technique to reveal the respective distribution of the fatty and fibroglandular tissues. The investigation of the relationship between cancer risk and breast parenchymal pattern will only be meaningful when the parameters can be reliably measured. MRI provides three dimensional images of the breast, and that allows for the slice-by-slice segmentation of the fibroglandular and the fatty tissues for the evaluation of breast parenchymal pattern. To date, only a few studies have investigated the percent breast density using MRI, and the relative distribution pattern of the fatty and fibroglandular tissues has not yet been reported. The wealth of the three dimensional information that can be provided by MRI has yet to be fully explored. With the establishment of the American Cancer Society guidelines for annual MRI screening for high-risk women, many more clinical breast MRI examinations will be performed. Development of reliable methods to measure the extent of density and to characterize the parenchymal pattern may provide additional information contributing to a better management plan for these women.